Improved Dutch Roll Stability Augmentation System for a Modified C-135B Aircraft
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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A stability augmentation system was designed for a C-135B aircraft which is modified by the installation of a large external fairing. Aerodynamic data for the modified C-135B were obtained from wind tunnel testing of the aircraft model. The SAS consists of the basic Boeing series yaw damper augmented with lateral acceleration feedback. Analysis and design were done using root locus techniques. The aircraft was then simulated on the analog computer to verify the design and make final system adjustments. Three flight conditions were simulated - two cruise conditions and power approach. In all the cases, the lateral-directional flying qualities were noticeably improved when the SAS was used. The biggest advantage of this particular SAS, namely, the acceleration feedback, is that both the damping ratio and the frequency of the Dutch roll were significantly increased without degrading flying qualities in some other area. As required, the SAS is simple and inexpensive, and requires a minimum of subsystem redesign. In addition to the requirement that the standard series yaw damper be installed, the SAS consists of only one accelerometer and one additional flap switch.
- Transport Aircraft